The present invention is related to a coupling structure of a flow control valve, and more particularly, to a coupling structure of a flow control valve for a blowby gas returning apparatus that is provided in an internal combustion engine.
FIG. 1 is a cross-sectional view showing a first example of a conventional flow control valve coupling structure 50 for a blowby gas returning apparatus (hereinafter a PCV valve). In the coupling structure 50, a fitting portion 62 of the PCV valve 61 is fitted axially to a coupling hole 60 that is provided in a cylinder head cover H. The PCV valve 61 is detachably coupled to the cylinder head cover H.
In the coupling structure 50, a cylindrical grommet 63 is first fitted to the coupling hole 60. Next, the fitting portion 62 of the PCV valve 61 is fitted to a mounting hole 63a of the grommet 63 thereby coupling the PCV valve 61 to the cylinder head cover H. The cylinder head cover H is required to undergo only machining to form the round coupling hole 60.
However, the fitting allowance of the fitting portion 62 requires high accuracy so that the fitting portion 62 of the PCV valve 61 does not fall out of the grommet 63. This increases the number of steps necessary for fitting the PCV valve 61 in the grommet 63.
FIG. 2 is a cross-sectional view showing a second example of a conventional PCV valve coupling structure 50A. The coupling structure 50A is disclosed in Japanese Unexamined Patent Publication No. 2000-161040. In the coupling structure 50A, a female thread is formed in a coupling hole 70 of the cylinder head cover H and a male thread is formed on a fitting portion 71 of the PCV valve 72. The PCV valve 72 is coupled to the cylinder head cover H by screwing the fitting portion 71 into the coupling hole 70. In the coupling structure 50A, it is not necessary to fit a grommet to the coupling hole 70. However, since the coupling structure 50A does not use a grommet, vibration of the internal combustion engine is transmitted directly to the PCV valve 72. Further, the machining of the female thread in the coupling hole 70 increases the number of steps required to couple the PCV valve 72 to the cylinder head cover H.